Reference will now be made in detail to various exemplary embodiments of the present application, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
A top view of the
The degree of underlap of the piezoelectric transducer 32 relative to diaphragm 30 may be expressed in terms of an underlap ratio, which in this case is the ratio of diameter Dp to diameter Dd. In some embodiments, the ratio of Dp to Dd may range from about 0.7 to about 0.99, and any ratio there between. In one embodiment, the Dp:Dd ratio ranges from about 0.8 to about 0.9. In yet another embodiment, the Dp:Dd ratio is about 0.85.
Underlapped piezoelectric actuator designs, such as that shown in the embodiment of
Jetting efficiency, as discussed herein, is defined as:
Volumetric displacement refers to the displaced volume of ink in the ink chamber, and drive voltage is the voltage applied to the jet driver. Thus, increasing jet efficiency lowers the required drive voltage necessary to achieve the same volumetric displacement of ink from the ink chamber. Reduced drive voltages are becoming more important as ink jet device densities continue to increase.
Reducing the dimensions of piezoelectric transducer 32 may also mitigate mechanical cross talk between adjacent actuators. Mechanical crosstalk results from the expansion and contraction of piezoelectric transducer 32, which can cause mechanical stresses across the print head that interfere with the functioning of adjacent devices.
Piezoelectric actuators having an underlapped design, such as the devices of the present application, can result in reduced mechanical crosstalk. For example,
The data in
Underlapped inkjet designs can also result in decreased sensitivity of the jetting voltage to misalignment of the piezoelectric transducer. In several solid inkjet designs, a relationship between piezoelectric misalignment and jetting voltage has been observed. For example, in some instances, the jetting voltage has been observed to increase by nearly 1.8 volts for every 1 mil that a piezoelectric transducer is misaligned relative to the diaphragm. This jetting voltage sensitivity to piezoelectric misalignment can result in undesirable variations in the jetting voltages employed to achieve consistent ink drop volumes between inkjet heads. In addition, if alignment varies greatly within a single head, the drive voltage needed by individual jets within the head will also vary greatly. Thus, piezoelectric misalignment can cause undesirable variations in jetting velocity and/or drop mass within the head.
Underlapping the piezoelectric transducer relative to the diaphragm can effectively reduce the sensitivity of the jetting voltage to misalignment of the piezoelectric transducer, and thereby mitigate the undesirable effects discussed above. Table 1, below, illustrates this effect. As shown in Table 1, as underlap increases, the voltage range, which is the difference between drive voltages for devices with perfect alignment and drive voltages for devices with 3 mils of misalignment, can significantly decrease. In devices having 1.5 mils of underlap, a voltage range of only 2.1 V occurs, which is significantly less than the voltage range of 5.3 V for devices having 1 mil of overlap.
The data in Table 1 is for devices having a rectangular shaped diaphragm and piezoelectric transducer, similar to the actuators shown in the devices of
Referring again to
The thickness of the piezoelectric transducer 32 can affect the desired width ratio of diaphragm 30 and piezoelectric transducer 32. This relationship is illustrated in
The thickness of diaphragm 30 can be any suitable thickness. In one embodiment, the thickness, Td, of diaphragm 30 ranges from about 1 micron to about 100 microns. In another embodiment, Td ranges from about 4 microns to about 8 microns. For example, Td can be about 6 microns.
The thickness of piezoelectric transducer 32 can be any suitable thickness. In one embodiment, the thickness, Tp, of piezoelectric transducer 32 ranges from about 1 micron to about 100 microns. In another embodiment, Tp ranges from about 6 microns to about 10 microns. For example, Tp can be about 8 microns.
Diaphragm 30 can be made out of any suitable material having adequate stiffness, strength and manufacturability. Examples of suitable materials include single crystal silicon, polysilicon, silicon nitride, silicon dioxide, stainless steel, aluminum, polyimide, nickel, glass, and epoxy resins.
Piezoelectric transducer 32 can be made of any ferroelectric or electrostrictive material, or any other material which changes physical dimension as the electric field in the material is changed. Examples of suitable materials include ceramics, such as lead-zirconium-titanate (PZT), lead-titanate (PbTiO2), barium-titanate (BaTiO3), lead-magnesium-niobium-titanate; or crystalline materials, such as zinc-oxide (ZnO), aluminum-nitride (AlN), quartz, lithium-tantalate (LiTaO3) and lithium-niobate (LiNbO2). Any suitable forms of these materials may be used, such as polycrystalline forms or single crystal forms. Other examples of suitable materials include polymeric materials such as polyvinylidene fluoride (PVDF) and its co-polymers. Piezoelectric transducer 32 can be deposited by any suitable method, such as screen printing or sol-gel techniques, both of which are well known in the art.
As mentioned above,
In accordance with the present application, the piezoelectric transducer 32 of the
In this embodiment, width, Wp, of the piezoelectric transducer 32 is shorter than width, Wd, of diaphragm 30, resulting in an underlap 31. Similarly, length, Lp, of the piezoelectric transducer 32 is shorter than length, Ld, of diaphragm 30. The underlap ratios of Wp to Wd and Lp to Ld may range from about 0.70 to about 0.99, and any ratio there between. In one embodiment, underlap ratios Wp:Wd and Lp:Ld both range from about 0.80 to about 0.90. In yet another embodiment, underlap ratios Wp: Wd and Lp:Ld are both about 0.85. The underlap ratios Wp: Wd and Lp:Ld can be the same or different.
Piezoelectric transducer 32 and diaphragm 30 need not have the same shape. For example, the major surface of diaphragm 30 on which piezoelectric transducer 32 is formed can be a rectangle, or other polygon, while the major surface of piezoelectric transducer adjacent the diaphragm 30 can have a circular or oval shape, and vice-versa.
Modeling of a device having the design shown in
Modeling results of the performance characteristics of the device of Example 1 are obtained by applying a simple bi-polar waveform to the model.
The results of modeling the performance characteristics for this example are shown in
This example shows that an underlapped actuator can be the basis for a small but efficient single jet design to support large nozzle packing densities with low voltage operation.
For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
It is noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the,” include plural referents unless expressly and unequivocally limited to one referent. Thus, for example, reference to “an acid” includes two or more different acids. As used herein, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.
While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or can be presently unforeseen can arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they can be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.